平茬措施对柠条生理特征及土壤水分的影响

通过对比试验,研究了平茬措施对柠条的净光合速率、蒸腾速率、水分利用效率、枝水势,以及土壤水分含量的影响。结果表明:(1)平茬措施对柠条生理特征的影响因其生长发育阶段而异。其中,在花期(6月份),平茬柠条日平均净光合速率较对照(未平茬柠条)降低14.72%,日平均蒸腾速率提高27.31%,水分利用效率较对照低33.33%;随着柠条的生长发育(7月、8月、9月),平茬柠条日平均净光合速率逐渐升高最终高于对照,日平均蒸腾速率的差距也不断缩小;相应的其水分利用效率增加较快(对照柠条、平茬柠条增幅分别达108.3%、222.5%),至自然生长末期(9月),平茬柠条较对照高出4.76%。(2)平茬柠条枝水势的日变化和月变化均高于对照。(3)在整个生长季,平茬柠条地的平均土壤含水量在50—240 cm范围内均明显高于对照,且平茬措施显著降低了0—300 cm剖面各层土壤水分变异情况。(4)相关分析显示,平茬措施对柠条生理特征及土壤水分有重要影响。可见,采取平茬措施的第1年,平茬措施对柠条同时产生消极的生理影响和积极的土壤水分效应。弄清平茬措施的更新复壮机理,需要开展更多的深入研究工作。

Effect of pruning measure on physiology character and soil waters of Caragana korshinskii

Caragana korshinskii Kom. sprouts readily when the stems are browsed by animals and is widely distributed in the China Loess Plateau and Hexi Corridor. C. korshinskii is a very ecologically adaptable shrub with an extensive root system capable of adsorbing large amounts of water and resistant to adverse environmental conditions. It is also very useful as forage and fuel wood. However, C. korshinskii degrades after 6-8 years as the branches die back and it is attacked by serious insect pests, decreasing its economic and ecological value. Pruning was used to stimulate regeneration of C. korshinskii, and resulted in desirable effects. Leaves and branches of C. korshinskii grew rapidly after cutting. However, little is known about the interaction between pruning and the rapid growth, and this lack of knowledge inhibits progress in managing planted shrublands. This study compares unpruned (control) to pruned (treatment) C. korshinskii plants to study the effects of pruning on the photosynthetic rate, transpiration rate, water use efficiency, the branch water potential for this kind of plant, and soil moisture content. First, the results show the effects of pruning on the physiological characteristics of C. korshinskii varied at different stages of growth. During the June flowering season, the net diurnal photosynthetic rate and water use efficiency of pruned C. korshinskii declined by 14.72% and 33.33%, respectively, when compared with the control. The corresponding diurnal transpiration rate of pruned plants increased by 27.31% compared with the control. With the onset of the growing season, July to September, the net photosynthetic rates of pruned C. korshinskii gradually increased and finally exceeded the rate of the control. At the same time, the difference between the transpiration rates of the two groups decreased. Water use efficiency of the pruned plants increased quickly during the growing season, by 222.5% overall, while water use efficiency of the control increased by only 108.3%. By September, the water use efficiency of the pruned plants was 4.76% higher than the control. Second, the branch water potential of the treated plants was higher than the control during the entire growing season, both daily and monthly. Third, during the entire growing season except for May, the average soil moisture remained higher for the pruned plants when compared with the control treatment at a depth of 50-240 cm, while the variation of soil moisture was minor at the depths of 0-50 cm and at 240-300 cm. Fourth, the correlation coefficients between net photosynthetic rate and transpiration rate of both the pruned and unpruned plants increased from the beginning of the flowering season (June) through the growing season into September. The correlation analysis shows pruning significantly and negatively affects the physiological properties of C. korshinskii while positively affecting soil moisture during the first growing season after pruning. More research is needed to understand the mechanisms involved in increasing the vegetative re-growth capacity of pruned C. korshinskii.